Panel supporting and lifting device

ABSTRACT

A panel feeding machine for removing the bottom panel from an upstanding stack of panels. A supporting and lifting device is provided for laterally supporting the stack and for lifting at least a portion thereof. The supporting device includes a pair of upstanding and spaced guide walls separated by the stack. The supporting device is secured to a frame which is adapted to permit a lateral movement of the guide walls with respect to the frame so that stacks of different widths may be accommodated. The lifting device is mounted on each of the guide walls and is movable therewith. The lifting device includes a jaw assembly mounted for lateral movement with respect to the guide walls for gripping the stack therebetween and lifting the upper portion of the stack to remove the weight of the upper portion of the stack from the lower panels thereof. A control is provided for controlling the gripping force of the jaw assembly in response to the weight of the upper portion of the stack.

United States Patent VanLinder et al.

PANEL SUPPORTING AND LIFTING DEVICE Inventors: Ronald C. VanLinder, Watervliet;

Basil R. VanLinder, Kalamazoo, both of Mich.

Winkel Machine Company, Inc., Kalamazoo, Mich.

Filed: June 23, 1972 Appl. No.: 265,505

Assignee:

References Cited UNITED STATES PATENTS Primary Examiner-Samuel F. Coleman Assistant Examiner-Joseph J. Rolla Anorney-Woodhams, Blanchard & Flynn 57 ABSTRACT A panel feeding machine for removing the bottom panel from an upstanding stack of panels. A supporting and lifting device is provided for laterally supporting the stack and for lifting at least a portion thereof. The supporting device includes a pair of upstanding and spaced guide walls separated by the stack. The supporting device is secured to a frame which is adapted to permit a lateral movement of the guide walls with respect to the frame so that stacks of different widths may be accommodated. The lifting device is mounted on each of the guide walls and is movable therewith. The lifting device includes a jaw assembly mounted for lateral movement with respect to the guide walls for gripping the stack therebetween and lifting the upper portion of the stack to remove the weight of the upper portion of the stack from the lower panels thereof. A control is provided for controlling the gripping force of the jaw assembly in response to the weight of the upper portion of the stack.

8 C, 7 Drawing Figures Patented Aug. 14, 1973 3 Sheets-Sheet 1 Patented Aug. 14, 1973 3 Sheets-Sheet 2 Patented Aug. 14, 1973 C5 Sheets-Sheet 5 PANEL SUPPORTING AND LIFTING DEVICE FIELD OF THE INVENTION This invention relates in general to a panel feeder and, more particularly, relates to a panel feeder having an improved panel lifting means.

BACKGROUND OF THE INVENTION The device of the invention was developed as a result of needs in battery plate handling equipment and will be described hereinbelow in terms of such usage. However, this description will be recognized as being for purposes of illustration only and will not be taken as limiting. Thus, it will be recognized that the device of the invention may be used in handling other types of panel-like articles.

The present invention was developed in a continuing effort to improve existing battery plate feeding machines, such as the battery plate feeding machine illustrated in US. Pat. No. 3,206,066.

Particularly there has long been a problem in the handling of relatively fragile panel-like articles in the generalmanner shown in the above-mentioned patent in that the means by which the major portion of the stack was lifted to free the bottom panel for ejection from the stack often created a severe problem of damage to such panels. This problem was particularly acute in connection with battery plates of under .050 inch in thickness or in connection with relatively fragile battery separators. In previously known equipment for this purpose, the means engaging the stack to be lifted must necessarily engage same with a pressure sufficient to hold and lift the stack in its maximum loaded condition. With battery plates of 0.050 inch in thickness or more, this presented no serious problem even when the stack was nearly exhausted so that only a few such battery plates received the pressure of the lifting mechanism. However, it has never in the past been possible, or at least possible without risk of damage, to apply such mechanism to battery plates of lesser thickness or to relatively fragile separators. In such cases the gripping force required when a full stack is present in the machine is such that when the stack has been substantially reduced in height, there is serious danger that the panels will be bent by the gripping means and hence not capable of feeding properly.

Accordingly, the objects of the invention include:

1. To provide an improved panel feeder including improved stack lifting means.

2. To provide an improved panel feeder as aforesaid which is particularly adaptable to stacks of relatively weak panels such as battery grids of less than 0.050 inch in thickness.

3. To provide a panel feeder, as aforesaid, which is adjustable to stacks of panels of differing dimensions. capable of containing stacks incorporating large numbers of panels, capable of lifting the panels above the lowermost one thereof off the lowermost panel to allow substantially free movement of the lowermost panel away from the stack and to continue such operation until all of the panels in the stack has been so removed.

4. To provide a panel feeder, as aforesaid, particularly adapted for use with battery plates and wherein the action of the panel lifting device is sufficiently gentle as to substantially eliminate damage to the plate.

5. To provide a panel feeder, as aforesaid, having a minimum number of adjustments for adapting to differing operating conditions, which adjustments are noncritical and easily effected, which panel feeder once adjusted, will remain in adjustment throughout long periads of operation, which is sturdily constructed, which requires only a minimum of maintenance over a long service life and which is easily and inexpensively maintained.

6. To provide a panel feeder, as aforesaid, which is relatively easily and inexpensively manufactured and .uses either widely available or easily fabricated parts.

7. To provide a panel feeder, as aforesaid, wherein the force utilized to grip the stack of panels and lift same from the lowermost one of the stack of panels is variable in response to the weight of the stack of panels that is lifted vertically off the lowermost panel.

Other objects and purposes of the invention will be apparent to persons acquainted with apparatus of this general type upon reading the following specification and inspecting the accompanying drawings, in which:

FIG. 1 is a perspective view of a panel feeder embodying the invention;

FIG. 2A is a sectional view taken along the line II--II of FIG. 1.

FIG. 2B is a sectional view similar to the sectional view of FIG. 2A except that the movable components have been moved so that a portion of the stack of panels is lifted off the lowermost ones thereof;

FIG. 3 is a sectional view taken along the line Ill-Ill of FIG. 2A;

FIG. 4 is a sectional view taken along the line lV-IV of FIG. 2A;

FIG. 5 is a sectional view taken along the line V--V of FIG. 4; and

FIG. 6 is an enlarged perspective showing of a portion of FIG. 1.

Certain terminology will be used in the following descriptions for convenience in reference only and will not be limiting. The words up, down, right and left will designate directions in the drawings to which reference is made. The words front and rear will refer to the front and rear sides of the panel feeder, the rear side being illustrated in FIG. 1. The words in and out will refer to directions toward and away from, respectively, the geometric center of the device and designated parts thereof. Such terminology will include the words above specifically mentioned, derivatives thereof and words of similar importance.

SUMMARY OF THE INVENTION In general, the objects and purposes of the invention are met by providing a supporting and lifting device for lifting a predetermined portion of a stack of panels. The device includes a pair of upstanding guide walls on either side of the stack andmounted onto frame means which is adapted to permit a lateral adjustment of the guide walls relative to the frame so that stacks of differing widths may be accommodated. The device also includes a lifting device mounted upon each of the guide walls and movable therewith. Each lifting device includes a jaw assembly mounted for lateral movement with respect to the guide walls for gripping the stack therebetween and lifting the upper portion of the stack to remove the weight thereof from the lowermost panel of the stack. The device also includes a control for controlling the gripping force of the jaw assembly in response to the weight of the upper portion of the stack.

DETAILED DESCRIPTION This invention relates to an improvement in a panel feeding machine illustrated in US. Pat. No. 3,206,066. Accordingly, reference is to be made to this patent for further details of the panel feeding machine. The following discussion will relate specifically to the improvement with only a general discussion relating to the supporting structure of the machine.

Referring to FIG. 1, the panel feeding machine comprises a generally horizontal table 11 and an upstanding frame member 12 defining a mounting surface 13 which extends generally perpendicularly upwardly from the table 11.

A pair of horizontally spaced guide walls 16 and 17 are secured to the mounting surface 13 by bolts 18 and 19, respectively. The guide walls 16 and 17 are pivotal, upon loosening of the bolts 18 and 19, about the axes of the bolts 18 and 19. Generally, however, it is not necessary that the bolts 18 and 19 be snugged up tightly due to the fact that the weight of the panels supported therebetween will serve to prevent a pivoting of the guide walls 16 and 17 as will be explained in more detail below.

Since each of the guide walls 16 and 17 are identical to each other except that the guide wall 17 is the mirror image of the guide wall 16, only the components of the guide wall 16 will be described in detail but when described, the components of the guide wall 17 will be re ferred to by the same reference numerals designating corresponding parts of the guide wall 16 but with the suffix A added thereto.

The guide wall 16 comprises a sandwiched arrangement of components. More particularly, the guide wall 16 comprises a pair of flat and parallel plates 21 and 22 (FIG. 4) separated by a pair of elongated and spaced bars 23 and 24. A chamber 26 is defined by the spaced plates 21 and 22 and the spaced bars 23 and 24. The guide wall 16 further comprises an additional plate 27 (FIG. 4) separated from the plate 22 by a pair of elongated and spaced bars 28 and 29. A chamber 31 is defined by the spaced plates 22 and 27 and the space bars 28 and 29. The plate 21, 22 and 27 and the bars 23, 24, 28 and 29 are all secured together by a plurality of screws 32 (FIG. 1). A plate 33 is secured to the lower end of the plates 21, 22 and 27 and the bars 23, 24, 28 and 29 as illustrated in FIGS. 1, 2A and 2B. The plate 33 extends laterally beyond the planar surface of the plate 27 as illustrated in FIGS. 1 and 4.

The guide walls 16 and 17 are mounted so that the plates 21, 21A, 22, 22A, 27 and 27A extend perpendicularly to the mounting surface 13 of the frame 12.

Each guide wall 16 and 17 has a lifting device 36 and 37 (FIG. 1), respectively, which is movable with the guide walls about the axis of the bolt 18 and 1.9 as well as being capable of moving laterally with respect to the guide walls. Since the lifting devices 36 and 37 are identical, only the lifting device 36 will be described in detail, but when described, the parts of the lifting device 37 will be referred to by the same reference numerals designating corresponding parts of the lifting device 36 but with the suffix A added thereto. The lifting device 36 comprises a vertically movable and laterally movable plate 38 (FIG. 2A) which is positioned in the chamber 31 between the plate 22 and 27. A pair of jaws 39 and 41 (FIG. 1) are secured to the plate 38 adjacent the lower edge thereof as illustrated in FIG.

2A. Openings 42 and 43 are provided in the plate 27 and the jaws 39 and 41 project therethrough when in the extended position and retract thereinto when in the retracted position as will be explained below. A block 44 is secured to the plate 27 adjacent the upper edge thereof by a bolt 46. The block 44 serves to loosely hold the plate 38 against the plate 22 of the guide wall 16 adjacent the upper end of the plate 38. The lower end of the plate 38 is, however, capable of moving about what is in effect a pivot axis defined by the in tersection between the plate 38 and the block 44 so that the jaws 39 and 41 can move into and out of the openings 42 and 43 in the plate 27.

A flange 47 is secured to the plate 38 adjacent the upper edge thereof by a screw 48. The flange 47 is cantilevered over the upper edge of the plates 21 and 22. A threaded opening 49 is provided in the flange 47. A threaded adjustment screw 51 is threadedly received in the threaded opening 49, the lower end of the adjusting screw 51 engaging the upper surface of a flange 52 secured to the plate 21 by a plurality of screws 5.3.

Referring now to FIG. 3, a pair of screws 54 and 56 are secured to the end of the flange 47 and project outwardly from the ends thereof. A pair of screws 57 and 58 are secured to the bars 23 and 24, respectively, and project inwardly therefrom toward each other. A tension spring 59 is secured to and extends between the screws 54 and 57. Similarly, a tension spring 61 is secured 'to and extends between the screws 56 and 58. The tension springs 59 and 61 bias the plate 38 to the lowermost vertically movable position and the magnitude of such bias is controlled by the adjustment of the adjusting screw 51".

A cam member 62 (FIGS. 2A and 2B) is secured to the plate 38 on the opposite side thereof from the jaws 39 and 41. The cam member 62 has a downwardly facing cam surface 63 which extends upwardly and away from the plate 38. The angle of inclination in this particular embodiment is 45 and has been found to produce the optimum result, however, an angle of inclination within the range of approximately 30 to 60' would be entirely feasible. The cam member 62 extends through an opening 64 (FIG. 2A) in the plate 22 into the chamber 26. The cam member 62 also has a cam surface 66 which is upwardly facing and is inclined upwardly and away from the same side of the plate 38 as does the cam surface 63. A portion 67 of the cam surface 66 extends generally horizontal as illustrated in FIG. 2A.

An opening 68 (FIG. 2A) is provided in the plate 21 adjacent the lower edge thereof. The opening 68 communicates with the chamber 26. An L-shaped actuating member 69 is received in the chamber 26. The L- shaped actuating member 69 comprises a pair of L- shaped side members 71 and 72. The L-shaped side members 71 and 72 each comprise an elongated leg 73 which is received in the chamber 26 and a relatively short leg 74 which extends outwardly of the chamber 26 through the opening 68. A plurality of rollers 76 are rotatably secured to the legs 73 (FIG. 3) and are received between the plates 21 and 22'(FIGS. 2A and 4). In this particular embodiment, there are two vertically spaced sets of two rollers 76 (FIG. 3) in order to stabilize the movement of the actuating member 69 vertically within the chamber 26. A roller 77 (FIG. 4) is rotatably secured between the legs 74 of the short legs 74 of the side members 71 and 72. The roller 77 is engaged by a vertically movable and vertically driven pusher member 78 which forms a part of the conventional panel feeding machine and as illustrated in the above-mentioned U.S. Pat. No. 3,206,066.

A roller 79 (FIG. 3) is rotatably secured between the vertically extending legs 73 on the side members 71 and 72. The roller 79 is positioned to engage the cam surface 63 on the cam member 62. A second roller 81 is rotatably secured between the vertically extending legs 73 of the side members 71 and 72 and positioned to engage the cam surface 66 on the cam member 62. The slope of the cam surfaces 63 and 66 and the diameter of the rollers 79 and 81 are chosen so that the rollers 79 and 81 remain in generally a close relationship to the cam surfaces 63 and 66, respectively. This close spacing minimizes to an acceptable amount any relative movement occurring between the actuating member 69 and the cam member 62 before the jaws 39 and 41 are urged inwardly toward the stack S.

A pin 82 is fixedly secured to the legs 73 of the side members 71 and 72 adjacent the upper ends thereof and projects through an elongated slot 83 in the plate 21. A manually operated lever 84 is pivotally secured to the plate 21 by a-screw 86 as illustrated in FIG. 2A and serves to permit a manual lifting of the actuating member 69 in accordance with the teaching in the aforementioned U.S. Pat. No. 3,206,066. A recess 87 (FIG. 2A) in the lever 84 is adapted to receive the outer end of the pin 82 to lock the actuating member 69 in the elevated position. The lever 84A is identical to the lever 84 as illustrated in FIG. 1 and a detailed description with respect thereto is believed unnecessary.

Each of the guide walls 16 and 17 is provided with a floating orifice mechanism 88 (FIGS. 1 and 6) which is designed to limit the number of panels that are fed by the panel feeding mechanism. Since the floating orifice mechanism 88 is identical to the floating orifice 88A except that one is the mirror image of the other, only the orifice 88 will be described in detail. More specifically, referring now to FIG. 5, the floating orifice mechanism 88 comprises an inverted T-shaped support member 89 having a vertical stem portion 91 and a lower cross bar portion 92. The stem 91 (FIG. 4) is received between the outer edges of the plate 21 and 22 adjacent the bar 24. A pair of vertically spaced rollers 93 and 94 are rotatably secured to the stem 91 (FIG. 5 and are guided by the inwardly facing surfaces of the plates 21 and 22. The right end (FIGS. 5 and 6) of the cross portion 92 is provided with a flange 96 which extends at a right angle thereto as illustrated in FIG. 4. The left end (FIG. 5) of the cross portion 92 has a bracket 97 secured thereto, as by welding. A lever arm 98 is pivotally secured to the bracket 97 by a bolt connection 99. The right free end of the lever 98 has a flange 101 (FIG. 6) secured thereto and extends at a right angle to the lever 98. The vertical spacing between the flanges 96 and 101 define an orifice 102. The orifice 102 may be adjusted by the adjustment mechanism 103 which comprises an internally threaded block 104 fixedly secured to the cross portion 92 of the T- shaped support member 89 and an internally threaded block 106 fixedly secured to the lever 98. An adjusting screw 107 is threadedly engaged with the internally threaded openings in the blocks 104 and 106 so that the dimension of the orifice 102 can be adjusted. The floating orifice mechanism 88 is resiliently supported on the guide wall 16 by a spring 108 which is secured at one end to the cross bar portion 92 of the T-shaped support member 89 by a screw 109 and at the opposite end by a screw 1 11 secured to the bar 29 separating the plates 22 and 27. The guide surface 112 on the flange 101 is spaced slightly above the upper surface of the plate 33 so that the surface 112 will be biased by the spring 108 into engagement with the lowermost one of the panels of the stack S.

OPERATION Although the operation of the device will be apparent to skilled persons, the following is a brief description thereof which is given for convenience.

A stack S of flat panels P is placed between the guide walls 16 and 17 and rests on the main shuttle mechanism 115 (FIG. 1) of the panel feeding machine 10. The edges of the panels P are supported on the upper surfaces of the plate 33 and 33A. The spacing between the lower ends of the guide walls 16 and 17 is regulated by adjustable stop mechanisms 1 16 and 117 which both have adjusting screws 1 18 and 119, respectively, which engage the surface of the plates 21 and 21A to limit the pivotal movement of the guide walls 16 and 17 about the axes of the bolts 18 and 19.

The sequence of operation is started by the pushers 78 and 78A moving the L-shaped actuating members 69 and 69A simultaneously vertically upwardly in the chambers 26 and 26A of the guide walls 16 and 17, respectively. Referring now to the internal structure of the guide wall 16, it being understood that the operation of the internal structure of the guide wall 17 is the same, the roller 79 is caused to move upwardly from the position illustrated in broken lines in FIG. 28, to the position illustrated in solid lines to thereby effect an upward and inward movement of the jaws 39 and 41 into engagement with the edge of the stack S. The upward movement of the plate 38 is resisted by the springs 59 and 61. This insures an initial inward movement of the jaws 39 and 41 in response to the connection between the roller 79 and the cam surface 63. The weight of the upper portion of the stack S which is lifted regulates the distance that the roller 79 moves along the cam surface 63 of the cam member 62. The greater the distance that the roller 79 moves along the cam surface 63, the greater is the distance that the jaws 39 and 41 are urged inwardly. Thus, if the weight of the upper portion of the stack S is great as would be the case with a large number of panels P, the jaws 39 and 41 will be urged into engagement with the edges of the panels with a sufficient amount of force to lift same by reason of the fact that the roller 79 will move along the cam surface 63 to a sufficient degree to cause the jaws 39 and 41 to lift the stack 8 rather than slip relative thereto. In other words, it is believed evident that with a heavy stack, the roller 79 will cause enough lateral inward movement of the jaws 39 and 41 so as to grip the stack with enough force to lift same whereas, with a lighter weight stack, it will not be necessary to generate as much laterally inward force and the roller will only cause enough lateral movement to cause the jaws 39 and 41 to grip the stack.

In this way the lifting mechanism can work effectively for both thick (as 0.090 inch thick) grids and for thin (as 0.050 inch thick) grids and will be selfadjusting as required to lift the stack. Particularly, when a small stack of thin grids is present the gripping force will diminish appropriately to avoid bending the grids though still providing enough force for lifting them as required.

After the upper portion of the stack S has been lifted as shown in FIG. 23 to create a gap (3 between the upper and lower portions of the stack S, thereby relieving the load from the lowermost panels in the stack, the main shuttle mechanism 115 can then cause the lowermost panel to move from the bottommost position of the stack into another portion of the panel handling machine as set forth in greater detail in the aforementioned US. Pat. No. 3,206,066. The floating orifice mechanism 88 accurately limits the number of panels that are fed from the stack into the other portion of the machine. The orifice 102 is adjusted by the adjusting screw 107 so that only one panel is fed at a time. This is accomplished by the flange 101 of the floating orifice mechanism 88 being biased upwardly by the spring 108. Thus, the flange 101 is always urged into engagement with the lowermost one of the panels in a stack. Accordingly, the upper flange 96 will prevent the next upper one of the panels to be driven from the stack into the other part of the machine. This is of particular value since it often happens that little hairs of battery plate material cause one or more grids to become hooked together so that when the shuttle mechanism 1 acts to move one panel from one portion of the machine, the intergripping of the hairs cause more than one panel to move in response to the shuttle. The orifree as described positively overcomes this tendency and assures that only one panel is fed at a time.

When the pushers 78 and 78A return to the original retracted position, the L-shaped actuating members 69 and 69A and the plate 38 are caused to move downwardly under the influence of gravity and by the springs 59 and 61 so that the roller 81 engages the cam surface 66 to both move the plate 38 downwardly as well'as inwardly of the guide wall 16 so that the jaws 39 and 41 are retracted from engagement with the stack S. Thus, the assembly is now ready for a next cycle of operation, which cycle of operation is identical to that described hereinabove.

Although a particular preferred embodiment of the invention has been disclosed in detail for illustrative purposes, it will be recognized that variations or modifications of the disclosed apparatus, including the rearrangement of parts, lie within the scope of the present invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a supporting and lifting device for lifting an upstanding stack of panels off the lowermost panels in the stack, said supporting and lifting device having a pair of upstanding and spaced guide walls separated by said stack and frame means for supporting said guide walls and lift means mounted upon each of said guide walls and including jaw assembly means mounted for lateral movement with respect to said guide walls for gripping said stack therebetween and lifting the upper portion of said stack to remove the weight thereof from the lower panel of said stack, the improvement comprising:

control means for controlling the gripping force of said jaw assembly means in response to said weight of said upper portion of said stack.

2. The supporting and lifting device according to claim 1 wherein said control means comprises means defining a cam surface on each of said jaw assembly means, said cam surface means being on a side of said jaw assembly means opposite to said stack and being downwardly facing and inclined upwardly laterally away from said stack; and

wherein said lift means comprises an upwardly acting actuating member engaging said cam surface means to both lift said jaw assembly means and urge said jaw assembly means into engagement with said stack at a force proportional to said weight of said upper portion of said stack.

3. The supporting and lifting device according to claim 2, wherein each of said jaw assembly means comprises a vertically and laterally movable plate having a jaw secured thereto on one side thereof and movable therewith; and

wherein said cam surface means is secured to the opposite side of said plate.

4. The supporting and lifting device according to claim 3, wherein said cam surface means and said jaw are generally horizontally aligned; and

wherein said actuating member engages said cam surface means at a location which is generally horizontally aligned with said jaw.

5. The supporting and lifting device according to claim 4, wherein said jaw assembly means includes resilient means for biasing said plate to the lowermost, at rest position.

6. The supporting and lifting device according to claim 2, wherein said actuating member is a roller.

7. The supporting and lifting device according to claim 2, wherein said control means includes means defining a second cam surface on the side of said jaw assembly means opposite to said stack and being upwardly facing and inclined upwardly laterally away from said stack; and

wherein said lift means comprises a downwardly acting actuating member engaging said second cam surface means to both lower said jaw assembly means and urge said jaw assembly means out of engagement with said stack.

8. In a panel feeding machine for removing the bottom panel from an upstanding stack of panels and including means for laterally supporting said stack and for lifting at least a part thereof, said means comprising:

a frame;

a pair of laterally spaced substantially upstanding guide walls for laterally supporting said stack therebetween;

jaw means mounted for lateral movement on each of said walls and for movement upwardly and downwardly therealong;

means carried by each of said walls for effecting said lateral movement of said jaw means with respect to said wall simultaneously when said jaw means is moved vertically with respect to said wall and at a force which is proportional to the weight of said part of said stack; and

energizing means for vertically moving said jaw means. 

1. In a supporting and lifting device for lifting an upstanding stack of panels off the lowermost panels in the stack, said supporting and lifting device having a pair of upstanding and spaced guide walls separated by said stack and frame means for supporting said guide walls and lift means mounted upon each of said guide walls and including jaw assembly means mounted for lateral movement with respect to said guide walls for gripping said stack therebetween and lifting the upper portion of said stack to remove the weight thereof from the lower panel of said stack, the improvement comprising: control means for controlling the gripping force of said jaw assembly means in response to said weight of said upper portion of said stack.
 2. The supporting and lifting device according to claim 1 wherein said control means comprises means defining a cam surface on each of said jaw assembly means, said cam surface means being on a side of said jaw assembly means opposite to said stack and being downwardly facing and inclined upwardly laterally away from said stack; and wherein said lift means comprises an upwardly acting actuating member engaging said cam surface means to both lift said jaw assembly means and urge said jaw assembly means into engagement with said stack at a force proportional to said weight of said upper portion of said stack.
 3. The supporting and lifting device according to claim 2, wherein each of said jaw assembly means comprises a vertically and laterally movable plate having a jaw secured thereto on one side thereof and movable therewith; and wherein said cam surface means is secured to the opposite side of said plate.
 4. The supporting and lifting device according to claim 3, wherein said cam surface means and said jaw are generally horizontally aligned; and wherein said actuating member engages said cam surface means at a location which is generally horizontally aligned with said jaw.
 5. The supporting and lifting device according to claim 4, wherein said jaw assembly means includes resilient means for biasing said plate to the lowermost, at rest position.
 6. The supporting and lifting device according to claim 2, wherein said actuating member is a roller.
 7. The supporting and lifting device according to claim 2, wherein said control means includes means defining a second cam surface on the side of said jaw assembly means opposite to said stack and being upwardly facing and inclined upwardly laterally away from said stack; and wherein said lift means comprises a downwardly acting actuating member engaging said second cam surface means to both lower said jaw assembly means and urge said jaw assembly means out of engagement with said stack.
 8. In a panel feeding machine for removing the bottom panel from an upstanding stack of panels and including means for laterally supporting said stack and for lifting at least a part thereof, said means comprising: a frame; a pair of laterally spaced substantially upstanding guide walls for laterally supporting said Stack therebetween; jaw means mounted for lateral movement on each of said walls and for movement upwardly and downwardly therealong; means carried by each of said walls for effecting said lateral movement of said jaw means with respect to said wall simultaneously when said jaw means is moved vertically with respect to said wall and at a force which is proportional to the weight of said part of said stack; and energizing means for vertically moving said jaw means. 